1. Technical Field
The present invention relates to the sterilization, seeding, culturing, storing, shipping, and testing of replacement cartilage tissue constructs. Specifically, the present invention relates to an apparatus and method for sterilizing cartilage constructs and then seeding and culturing the constructs with viable mammalian cells, resulting in constructs more likely to display the biochemical, physical, and structural properties of native cartilage tissue.
2. Discussion of the Related Art
Articular cartilage is responsible for providing moveable joints with the ability to perform smooth gliding motions. Articular cartilage consists of highly specialized cells (chondrocytes) surrounded by a dense extracellular matrix (ECM) consisting primarily of type II collagen, proteoglycan, and water. Resistance of the ECM to water flow gives cartilage the ability to disperse high joint loads by absorbing shock and minimizing stress on subchondral bone.
However, fully matured cartilage has limited ability for self renewal and repair. Thus, tissue damage from, for example, trauma or degenerative joint disease, can lead to continuous destruction of cartilage and eventually osteoarthritis. Due to the large number of orthopedic surgeries that are required to treat damaged cartilage, there is great demand for replacement cartilaginous tissue.
The seeding and culturing of tissue for use in replacement therapy is known in the art. For example, U.S. Pat. No. 5,266,480 to Naughton et al. discloses the establishment of a three dimensional matrix, seeding of the matrix with desired cells, and maintenance of the culture to provide a variety of three-dimensional tissues suitable for use in different applications.
Historically, the seeding and culturing of tissue has taken place in a static environment such as a Petri or culture dish. However, there are disadvantages to seeding and culturing tissue in such an environment. First, achieving acceptable seeding of cells throughout the thick cartilage tissue construct without forced convection, as exists in a static system, is difficult. Second, maintaining an adequate supply of nutrients to chondrocyte or related cells throughout a replacement cartilage tissue construct is difficult in a static system given the relative thickness (approximately 2-5 mm) and density of the microporous construct. Moreover, the density of the construct increases significantly during the seeding and culturing process as cells proliferate and fill interstitial spaces. Thus, the lack of circulation of nutrients in a static system results in a slow and ineffective seeding and culturing process.
In contrast, cells which are seeded and cultured in a dynamic environment are more likely to tolerate the physiological conditions which exist in the human body once implanted. This is because a culturing condition of periodic or continuous fluid flow and pressure more closely resembles the conditions under which articular chondrocyte cells are cultured in the human body, which will result in the formation of a tissue-engineered cartilage construct which possesses physical and biochemical properties that are similar to native cartilage. Thus, there exists a need for a dynamic environment in which to seed and culture replacement cartilage tissue constructs and other prosthetic devices.